Gwent's Police and Crime Commissioner and Gwent Police's former chief constable will appear before the Home Affairs Select Committee in London later.
Both parties will give their side of events that led to Mrs Napier's departure at the meeting in Westminister this afternoon.
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Healthy Air Cymru, a coalition of Welsh charities, have urged the Welsh Government to do more to tackle air pollution.
The findings are based on average earnings, house prices, access to services, crime figures, skill levels and unemployment figures.
Details of the road closures and train delays ahead of Ed Sheeran's concert over the next four evenings.